In recent years, reduction in rolling resistance of tires has been demanded from the perspective of fuel economy during travel of vehicles. From the perspective of safety, enhancement in wet performance (braking performance on wet road surfaces) has been also demanded. For these, a method of both achieving the low rolling resistance and the wet performance by blending silica to a rubber component constituting a tread portion of a tire has been known.
However, since silica has low affinity with rubber components and aggregability in silica is high, even when silica is simply added to a rubber component, silica is not dispersed, and there has been problems in that effect of reducing rolling resistance and/or effect of enhancing wet performance cannot be sufficiently achieved.
In response to these, International Patent Application Publication No. WO 2014/050341 discloses a conjugated diene rubber obtained by reacting a predetermined modifying agent with a conjugated diene-based polymer chain having an active terminal. International Patent Application Publication No. WO 2014/050341 describes that, by using the conjugated diene rubber, the affinity of silica and rubber is made excellent and the low heat build-up (low rolling resistance) and wet grip performance of tires can be enhanced.
When the inventors of the present technology studied the rubber composition including the conjugated diene rubber described in International Patent Application Publication No. WO 2014/050341, the inventors found that, depending on the compounded amount of the conjugated diene rubber and/or additives such as silica, the low rolling resistance and/or the wet grip performance of the produced tire may be poor, and also the steering stability may be poor.